The invention relates to servo systems, and more particularly to motion controlling and position sensing, and still more particularly to motion control systems employing accelerometers.
For background, reference is made to Dorf and Bishop, Modern Control Systems, Seventh Edition, 1995, Addison-Wesley Publishing Company, ISBN 0-201-50174-0, especially to Chapters 2, 4 and 8.
It is an important object of the invention to provide improved motion controlling.
In one aspect of the invention, a combining network in a closed loop feedback control system combines an acceleration signal (representing an acceleration of a movable element) and a position signal (representing a position of the movable element) to produce an inferred position signal (representing an inferred position of the movable element). The combining network includes a first signal processor for processing the acceleration signal to provide a processed acceleration signal and a combiner for combining the processed acceleration signal with the position signal to provide the inferred position signal.
In another aspect of the invention, in a closed loop feedback control system, a method for combining an acceleration signal and a measured position signal to provide an inferred position signal includes low-pass filtering the acceleration signal to provide a filtered acceleration signal and combining the filtered acceleration signal with the measured position signal to provide the inferred position signal.
In another aspect of the invention, apparatus for detecting position includes an accelerometer for providing an acceleration signal representative of acceleration, a position sensor for providing a position signal representative of position, a first processor for processing the acceleration signal to provide a modified acceleration signal, a combiner for combining the acceleration signal and the position signal to yield an inferred position signal representative of inferred position.
In another aspect of the invention, a motion control apparatus includes a movable element, an input for receiving a signal representative of a desired position of the movable element, a position sensor for providing a position signal representative of the position of the movable element, an accelerometer for providing an acceleration signal representative of the acceleration of the movable element, and a combining network for combining the position signal and the acceleration signal for providing an inferred signal representative of an; inferred position for the movable element. The combining network includes a first processor for processing the acceleration signal to provide a processed acceleration signal, a; combiner for combining the processed acceleration signal and the position signal to provide the inferred position signal, a summer for comparing the inferred position signal with the desired position signal to provide a control signal, and a mover responsive to the control signal for moving the movable element to reduce the difference between the inferred position and the desired position.
In still another aspect of the invention, a circuit for combining the acceleration signal and the position signal to provide the inferred signal includes an input for the acceleration signal; a first resistor having an input connected to the acceleration signal input; a first capacitor having an input connected to the output of the first resistor and having a grounded output; a second resistor having an input connected to the input of the first capacitor and the output of the first resistor; an input for the position signal; a third resistor having an input connected to the input for the position signal; a second capacitor having an input and an output, the input of the second capacitor connected to the output of the third resistor and the output of the second capacitor being grounded; a fourth resistor having an input connected to the input of the second capacitor and the output of the third resistor; an operational amplifier having an inverting input connected to the output of the second resistor and the output of the fourth resistor, the noninverting input of the operational amplifier being grounded; a fifth resistor having an input coupled to the output of the second resistor and the output of the fourth resistor; an output for the inferred signal coupled to the output of the fifth resistor and to the -output of the operational amplifier; and a fifth capacitor, connected in parallel with the fifth resistor.
A motion control system according to the invention is advantageous, because it greatly enhances the signal to noise ratio in providing the position signal, thereby enabling more accurate control of position in the presence of noise. Furthermore, in digital control systems, a motion control system according to the invention, is free of an anti-aliasing filter and consequently allows the faster sampling rates and greater bandwidth; because at high frequencies, the. invention uses the relatively high signal-to-noise ratio acceleration signal for providing the inferred position signal; and because at high frequencies the relatively low signal-to-noise ratio position signal is heavily filtered, thereby significantly attenuating noise.